In general, a friction material for a brake lining or a clutch facing which is applied to a torque transmission member such as an electromagnetic clutch, is prepared by adding a binder of thermosetting resin such as phenol resin to asbestos fiber, inorganic and organic fillers and an organic friction conditioner etc., performing a hot press forming of the mixture and then hardening the same. However, the public nuisance of asbestos dust has been recognized. As a result, a friction material not containing any asbestos fibers, is required not only for mobile applications but also for electromagnetic clutches for driving a business machine and an industrial machine.
The asbestos fibers are replaced by metallic fibers, glass fibers, ceramic fibers, synthetic fibers or the like, and a friction member made of steel fibers, known as a so-called semi-metallic pad, has been put into practice for mobile applications.
However, a semi-metallic pad made of steel fibers, is not applied in a friction member for an electromagnetic clutch, which must be made of a nonmagnetic substance. Further, although a friction material prepared of glass fibers has been used in a clutch plate in practice, such a material will not be of great utility in the future, since the raw material therefor is expensive and additionally inferior in its workability and handling.
Aramid fibers, which have recently being considered with interest, have been practically employed for making a friction member for mobile applications. However, wide spread use of aramid fibers is not expected because of the high cost, similar to the friction material made of glass fibers.
Thus, awaited is development of a non-asbestos friction material, which can be made of low-priced raw materials.